- Index types should be setable on a per question basis.
- the constructor and singleton() should accept an option/configuration array.
- addQuestion should accept be 3 parameters max, the third one being an option array (to prevent future API problems)
- maybe do the same with addRule(), unless you are sure it won't change.
- It should be possible to use a previous answer to setup the next questions. A page system like in QFC might work.
- What about an xml wizard definition ?
- Make sure every text is localizable.

-camelCase instance variables
I have looked through the CS guidelines, and I am familiar with the camelCase rule for method names. However, there is no rule that I could find regarding variable names. So, I've written variables_like_this and methodsLikeThis to make it very easy to tell them apart at a glance.

- Index types settable on per-question basis
This is a good idea, and I just realized I forgot to put it in alpha2. I will add this feature for alpha3.

- previous answer to setup next question
Unless I misunderstand you, this is already possible with the setNextQuestion methods. Both the Question and Answer classes have this method, allowing for a default next question, and the setting of a specific next question based on a specific answer.

- xml wizard definition
Good idea, I'm planning on this for a future release. I'd like to make the format compatible with the XML format used in defining post-install scripts in PEAR 1.4.0.

- localizable text
Done!

- addGroupRule empty
This is still on my to-do list. Working on a good way to handle this, and will include it in the next alpha release.